Which country is free for Vietnam Visa?

Almost all foreigners need an Entry visa to Vietnam except some included in the Vietnam visa exemption list below.

Vietnam Visa exemption is granted to:

Citizens of Cambodia, Thailand, Malaysia, Singapore, Indonesia and Laos for visits of 30 days at the maximum.
Citizens of Philippines for visits of 21 days at the maximum.
Citizens of Japan, South Korea, Sweden, Norway, Denmark, Russia and Finland for visits of 15 days at the maximum.
Citizens of Brunei, Myanmar for visits of 14 days at the maximum.
Citizens of France holding valid diplomatic or official passports for visits of 90 days at the maximum or several visits of 6 months at the maximum.
Citizens of Chile holding valid diplomatic or official passports for visits of 90 days at the maximum.
APEC Business Travel Card (ABTC) Holders from Asia-Pacific Economic Cooperation (APEC) member economies for visits of 60 days at the maximum.
For those who travel to Phu Quoc Island – Vietnam : Foreigners and Vietnamese nationals bearing foreign passports who enter Vietnam through an international border gate and then travel to Phu Quoc Island and stay in Phu Quoc less than 30 days will also be granted Vietnam visa exemption. Passports must be valid for at least 45 days. After arriving in Phu Quoc Island, if visitors want to travel to other localities or stay in the island for more than 15 days, the immigration department will be responsible for issuing visas right on the spot.

What is single entry visa?

Vietnam single e-visa (or visa) allows you to entry the country one time only, as soon as you leave the country after you have entered Vietnam, your visa will be cancelled and you cannot come back in again unless you applying for another new visa.